Letters to the Editor: 17OHP benefits prior preterm birth patients

Dr Charles Lockwood, one of the foremost authorities on preterm birth, has written a balanced and factual editorial laying out his view of progestin use today and in the future.¹ However, although his editorial speculates that vaginal progesterone might eventually replace hydroxyprogesterone caproate (17OHP) for reducing the risk of preterm birth, he still recommends 17OHP to treat prior preterm birth patients. Why this apparent contradiction?

The most obvious reason to recommend 17OHP is that current evidence demonstrates that vaginal progesterone is ineffective for patients with a prior preterm birth, but shows benefit for short cervix patients. The da Fonseca study using vaginal suppositories was only positive when an analysis excluding many patients was performed² and a second, larger study using vaginal gel was negative.³ The 2 prospective studies in which vaginal progesterone showed benefit enrolled women with a short cervix, which represents only about 2% of pregnant women.^4,5

Recent literature has documented the risks of serious neonatal morbidity in late preterm births. Hydroxyprogesterone caproate in the National Institute of Child Health and Human Development (NICHD) study⁶ is the only progestin shown to reduce the number of preterm births (defined as less than 37 weeks). Vaginal progesterone shifted early preterm births to late preterm births. Both the da Fonseca and O'Brien prior preterm birth studies showed no difference at less than 37 weeks when analyzed using the intent-to-treat principle.^2,3 The short cervix studies either did not report data after 34 weeks⁴ or showed no difference at less than 37 weeks.⁵ Further, a subanalysis of short-cervix patients in the DeFranco study showed no difference at less than 37 weeks.⁷ Therefore, no evidence currently exists that vaginal progesterone has any impact on late preterm birth, which represents the majority of preterm births. Only the NICHD study of 17OHP demonstrates benefit for prior preterm birth patients at early and late gestational ages.⁶

ROBERT BIRCH, PHD
DIRECTOR, CLINICAL SCIENCES KV PHARMACEUTICAL COMPANY